1. Field of the Invention
The present invention relates to systems and methods of three-dimensional (3-D) printing. More specifically, the present invention relates to systems and methods of 3-D printing for fabricating features on semiconductor devices and related components.
2. State of the Art
Over the past few years three-dimensional (3-D) printing has evolved into a relatively promising process for building parts. For example, 3-D printing has been used for the production of prototype parts and tooling directly from a computer-aided design (CAD) model.
Three-dimensional printing of solid structures utilizes a computer, typically under control of computer-aided design (CAD) software, to generate a 3-D mathematical model of an object to be fabricated. The computer mathematically separates, or “slices,” the model into a large number of relatively thin, parallel, usually vertically superimposed layers. Each layer has defined boundaries and other features that correspond to a substantially planar section of the model and, thus, of the actual object to be fabricated. A complete assembly or stack of all of the layers defines the entire model. A model which has been manipulated in this manner is typically stored and, thus, embodied as a CAD computer file. The model is then employed to fabricate an actual, physical object by building the object, layer by superimposed layer.
One particularly effective 3-D printing system, commercially available from Objet Geometries Ltd. of Rehovot, Israel, is the Eden 330®. In operation, the Eden 330® deposits a layer of photopolymer material via inkjet type of printer heads onto a support. For example, layers as thin as 16 μm at a 600×300 dpi (dot per inch) resolution may be deposited in a selected location using the printer heads currently available. After each deposition of the layer of photopolymer, an ultraviolet (UV) light is used to cure and harden each layer. The process is repeated by selectively depositing additional photopolymer to form an additional layer, followed by subsequent curing until the complete 3-D CAD model is formed. Other 3-D printing systems and methods are described in detail in U.S. Pat. Nos. 6,658,314; 6,644,763; 6,569,373; and 6,259,962 assigned to Objet Geometries Ltd., the disclosure of each of which patents is hereby incorporated herein in its entirety by this reference.
Conventionally, 3-D printing systems, such as the aforementioned Objet systems, have been used to fabricate freestanding structures. Such structures have been formed directly on a platen or other support system of the 3-D printing system. Complicated geometries having overhangs and undercuts may be formed by employing a support material, which the structure is formed on, followed by removing the support material by dissolving the support material in water. As the freestanding structures are fabricated directly on the support system and have no physical relationship to other structures at the time they are formed, there is typically no need to precisely and accurately position features of the fabricated structure. Accordingly, conventional 3-D printing systems lack image sensors for ensuring that structures are fabricated at specific, desired locations. However, precise and accurate positioning of features of structures fabricated using a 3-D printing system would be particularly important if the structures were to be 3-D printed, on or immediately adjacent to, another object, such as a semiconductor device, an assembly including a semiconductor device and other components, or an assembly incorporating one or more semiconductor devices carried, for example, on a carrier substrate such as a printed circuit board.
Stereolithography has been used in the past to form a variety of features on semiconductor assemblies, such as underfill and encapsulation structures. The stereolithography techniques employed typically involve immersing the semiconductor assembly to a predetermined depth in a liquid photopolymerizable resin and selectively curing portions of the liquid resin by rastering with a laser beam to form the desired structures. Examples of stereolithography systems suitable for forming a variety of features on a semiconductor assembly are disclosed in U.S. Pat. No. 6,537,482 to Farnworth and U.S. patent application Ser. No. 10/705,727 to Farnworth, both of which are assigned to the assignee of the present application. The disclosure of each of the foregoing documents is hereby incorporated herein in its entirety by this reference.
While the above-referenced Farnworth patent and patent application disclose forming a variety of different structures on a semiconductor assembly, the disclosed immersion-type stereolithography processes require the use of an excess amount of expensive photopolymer material. This is because only a portion of the liquid photopolymerizable resin is cured to form a structural element while the remaining liquid resin must be drained and cleaned from the semiconductor assembly. Furthermore, the processing time using immersion-type stereolithography systems is significantly slower than the processing time for a 3-D printing system, such as the aforementioned Objet systems.
Accordingly, there is a need for 3-D printing systems which are configured to form structures on substrates, such as semiconductor substrates and semiconductor device components, and which include systems for accurately positioning the fabricated structures during formation thereof.